STRONG CONTROLLABILITY AND OBSERVABILITY AND THEIR EFFECTS ON TRANSIENT STABILITY OF POWER SYSTEMS

ABSTRACT

An algorithm is developed for identifying bus clusters called control areas that have strong local controllability and observability property for measurements and controls at the buses or on generators within the control area. Two types of control areas are identified; one that is based on weak boundaries of the reactive power voltage jacobian and is called voltage control area; the other is based on the jacobian of both real and reactive power balance equations with respect to voltage and angle at network buses. The two control areas are identical under light load conditions, but are different as the system approaches voltage collapse or poorly damped low frequency oscillations. The understanding of strong controllability and observability in terms of real power angle dynamics and reactive power voltage dynamics (voltage control areas) and the strong controllability and observability of voltage and angle dynamics (control areas) helps understanding of voltage instability and inter-area oscillations.